I've noticed that in a lot of answers, the preg_match answer is selected as "the" answer far more often than the ctype_* answers are. Is there some kind of superiority to one over the other, objectively, or is it merely a matter of preference? The php manual doesn't seem to shed any light on it that I can see. And since I wouldn't actually understand much by getting my hands down into the brains of PHP, I'm really just interested to know if there's some kind of performance difference or other objective measurement.